A recording apparatus based on inkjet method (hereinafter referred to as “inkjet recording apparatus”) has been commonly known as an inkjet recording apparatus that can flexibly meet the demands for small batches of a variety of products. In the inkjet recording apparatus, ink is emitted from the nozzle provided on the surface of the recording head arranged face to face with the recording medium, and hits and fixes on the recording medium, whereby an image is recorded on the recording medium. Differently from the image recording means based on the conventional gravure printing or flexographic printing, this method does not require a plate making process, and is capable of meeting a low volume production requirement easily and quickly. This method is also characterized by less noise and easy recoding of a color image through the use of a multi-colored ink.
In recent years, an inkjet recording apparatus using a photocurable ink (e.g., Patent Document 1) is known as an inkjet recording apparatus capable of meeting the requirements of various types of recording media. This apparatus uses a photocurable ink containing a photo-initiator of a predetermined sensitivity to light such as ultraviolet rays, wherein the ink emitted onto a recording medium is cured by exposure to light and is fixed on the recording medium. In the inkjet recording apparatus using such a photocurable ink, the ink having reached the recording medium is instantly cured by exposure to light. This arrangement minimizes the possibility of ink penetrating the recording medium or bleeding thereon, and also ensures an image to be recorded on such recording media as plastic or metallic media that do not absorb ink at all due to lack of an ink receiving layer as well as on plain paper.
The aforementioned inkjet recording apparatus includes a serial print type inkjet recording apparatus that forms an image by the ink emitted from each recording head while scanning by reciprocal movement of the recording head in the main scanning direction, and by intermittent conveyance of a recording medium in the conveyance direction perpendicular to the main scanning direction. This serial print type inkjet recording apparatus has a problem of involving a difference in the color tone and glossiness of the recorded image in the main scanning direction between the movements of the recording head in the outward and homeward directions.
This is because, in the movements of recording head in the outward and homeward directions, there is a difference in the order of the colors of the ink emitted to the recording medium, and therefore, the expansion of dot diameter and cohesion of dots of the ink emitted later vary according to the degree of penetration, wettability and curing of the ink emitted earlier to the recording medium. The expansion of dot diameter and cohesion of the dots of ink depend on the difference in the timing of curing by exposure of light and the intensity of irradiated light.
In the conventional art, to resolve the difference in the color tone or glossiness of the recorded image in the main scanning direction, two sets of recording heads for emitting inks of a plurality of colors are provided symmetrically with respect to the main scanning direction so that difference does not occur to overlapping of inks in the outward and homeward movements in the main scanning direction (e.g., Patent Document 2).
Another conventional technique is found in the inkjet recording apparatus wherein an aqueous ink is used to record an image through adjustment of the ink emission volume (e.g., Patent Document 3).
However, the technique described in the Patent Document 2 requires that recording heads twice as many as the conventional ones should be mounted. This causes an increase in the size and weight of the apparatus.
In the technique described in the Patent Document 3, when an aquatic ink penetrating the recording medium is used, ink emission volume is adjusted in response to the degree of penetration of ink. This technique does not meet the requirements of the photocurable ink wherein there is almost no penetration of ink into the recording medium, and expansion of the ink dot diameter and the dot cohesion of ink depend on the differences in the timing of curing due to exposure to light or intensity of light to be applied.
[Patent Document 1] Unexamined Japanese Patent Application Publication No. 2001-310454
[Patent Document 2] Examined Japanese Patent Application Publication No. 3248704
[Patent Document 3] Unexamined Japanese Patent Application Publication No. 2003-25613